Hand machined mechanical pencils

Adjustable microscope eyepiece holder (18/12/13)

I recently got a great deal on a stereo microscope from EBay. It cleaned up nicely, but unfortunately the eyepieces don't have any diopter adjustment. Normally, it's possible to adjust the focus of one eyepiece independently from the main focus to correct for different eye strengths (e.g. my left is -4.5, but my right is -1.25). In fact, I strongly suspect that this microscope originally did have an adjustable eyepiece, but it has been swapped by someone for a fixed eyepiece (the 'scope was from a lot of three, so possibly parts were mixed around).

I decided to make an adjustable holder for the right eyepiece and also incorporate a reticle (aka graticule) holder, which is very useful for an inspection microscope. I got the reticle from Joy's Optics on EBay - go to the main store then search for "graticule". Both 20mm and 24mm diameter versions are available - I got the 20mm.

Here's a PDF which shows the individual parts (don't worry about any of the actual dimensions - some of these changed as I was making the parts). The colours and names mentioned below refer to the PDF.

The actual eyepiece itself is threaded (unlike standard eyepieces, which are just "drop-in"). This screws into a small tube (red, "eyepiece tube extension"). The reticle is placed in a threaded holder (cyan, "reticle holder (alum.)") and is held in place with a threaded brass ring. The reticle holder screws into the end of the eyepiece extension tube and is locked by another threaded ring. This allows the reticle to placed at exactly the focal point of the eyepiece so it is sharply superimposed on the image.

The eyepiece+reticle assembly drops into the end of another threaded tube (orange, "eyepiece adjustment tube"), which in turn is screwed on to the base (blue, "bottom mount"). By turning the eyepiece adjustment tube, it can be moved in or out to bring the main image into focus.

I made a couple of tools to grip the body and retaining rings during assembly. Several of the threaded joints are coated with high-viscosity damping grease to give smooth movement.

The pictures and assembly video should hopefully explain all this better!

All parts

Reticle holder

Eyepiece adjustment tube

Bottom mount

Clamping rings

Reticle assembly (I didn't have the actual reticle at the time, so that's a mockup with wire crosshairs)

Eyepiece and reticle assembled

Another view

Attached to bottom mount

Another view

Tool for gripping the main body during installation

Fitted on microscope


With eyepiece removed

View of the crosshairs

Video of assembly: